The present invention relates to a section bending machine.
The machine according to the present invention is a penetration-type bending machine for bending sections, in particular tubes, bars and similar, in a number of directions to shape the sections in space.
For the sake of simplicity, the following description refers specifically to cylindrical-section tubes, it being understood, however, that the penetration bending machine may be used for bending any type of section having a given axis and a constant cross section along the axis.
On penetration-type tube bending machines, the tube is fed through a fixed first annular die and a second annular die movable with respect to the first, and, as the tube is fed through, the second annular die is moved to bend the tube. The extent to which the second annular die is moved determines the curvature of the tube.
One known penetration-type tube bending machine described in U.S. Pat. No. 5,111,675 feeds the tubes longitudinally in a given first direction, and comprises a fixed first annular die; and a second annular die, which is moved by a movable assembly in the first direction and along a plane perpendicular to the first direction to bend the tube in a number of directions in a region between the first and second annular die, and is connected to the movable assembly by a spherical joint enabling the second annular die to rotate freely as a function of the curvature assumed by the tube.
The above machine has several drawbacks owing to the tube, as it is being bent, exerting friction on respective portions of the first and second annular die. The degree of friction depends on the amount of curvature, the type of material from which the tube is made, the type of material from which the first and second annular die are made, and the speed at which the tube is fed through the first and second annular die, so that, when fed in a given direction through the second annular die, the tube generates severe friction on a given portion of the second annular die, and rotates the second annular die, which, rotating freely with respect to the movable assembly, tends to move crosswise with respect to the cross section of the tube, thus crushing the tube. In short, as it is being bent, the tube is ovalized by the second annular die being rotated by the tube itself.
Moreover, once the machine has finished bending one tube, the movable assembly aligns the second annular die with the first in the first direction, but does not position the second annular die to permit insertion of the next tube, so that the second annular die must be positioned manually, which takes time and does not guarantee the degree of precision expected of this type of machine.
Ovalizing of the tube is further aggravated when the tube is not perfectly smooth. That is, chips or machining debris on the lateral surface of the tube may result in seizure, thus greatly increasing rotation of the second annular die and the extent to which the tube is ovalized.
It is an object of the present invention to provide a section bending machine designed to eliminate the drawbacks typically associated with the known state of the art.
According to the present invention, there is provided a machine for bending sections, in particular tubes, bars and similar, having a longitudinal axis and a constant cross section along the longitudinal axis; the machine feeding the sections longitudinally in a first direction, and comprising a first and a second annular die, and an assembly connected to the second annular die and movable in a plane perpendicular to the first direction to move the second annular die into a number of operating positions with respect to the first annular die to bend the sections; and the machine being characterized by comprising a joint connecting the first and the second annular die, and which forces the second annular die to assume a given position with respect to the first annular die for each position assumed by said assembly.